In addition to the normal speech service, modern mobile systems also provide subscribers with different data transmission properties, e.g. asynchronous bearer services or a facsimile Group 3 eleservice.
Data services usually employ a specified communication protocol within a mobile network. For example the European digital mobile system GSM (Global System for Mobile Communications) comprises a UDI-coded rate adaptation protocol based on CCITT V.110, and further a radio link protocol (RLP) for non-transparent services, and a GSM facsimile protocol. A digital connection from a mobile network to the fixed network, such as an integrated services digital network (ISDN) or a public switched telephone network (PSTN), may employ protocols different from the protocols within the mobile network. Examples of protocols include CCITT V.110 and V.120 rate adaptation protocols in the ISDN network, modem protocols (CCITT V.22, V.22bis, V.32), and facsimile Group 3.
A mobile system comprises adaptation functions for adapting a data connection set up within the mobile network to the protocols used by terminal equipments and other telecommunication networks. The adaptation functions typically include a terminal adaptation function (TAF) located at an interface between a mobile station and a data terminal equipment connected thereto, and an interworking function (IWF) at an interface between the mobile network and another telecommunication network, usually in connection with a mobile services switching centre. A mobile services switching centre usually comprises different types of adapter equipment pools for supporting different data services and protocols, for example a modem pool with modems and facsimile adapters for modem and facsimile services, a UDI/RDI rate adaptation pool, etc. FIG. 1 illustrates a GSM network comprising IWF adapter equipment pools in a mobile services switching centre (MSC).
The signalling within a mobile network usually supports the transmission of data-service-specific parameters. However, the signalling does not often support the transmission of these parameters in all the networks via which a call is routed. This happens for example when a call arrives from or is routed via the PSTN. In such a case, the mobile network should be able to conclude in some other manner the data service and the adapter equipment that an incoming call requires, for example.
A known solution to this problem is a multinumbering scheme where a mobile subscriber has as many MSISDN (mobile subscriber ISDN) numbers as he has different services to which he wants to receive incoming calls. In a multinumbering scheme, a calling subscriber dials the one of the mobile subscriber's MSISDN numbers that corresponds to the desired service. In the GSM system, the subscriber services are determined in the home location register (HLR) of the subscriber, which also stores permanently other subscriber data. The HLR also stores information on the correspondence between the MSISDN numbers and the services of the subscriber. The HLR also assigns to each MSISDN number a BCIE (bearer capability information element) that indicates the call type and the bearer services and protocol required in the call. The IWF can be configured according to this data. According to the current GSM recommendations (GSM TS 09.07), a subscriber has a dedicated MSISDN number for each service. A subscriber may have, for example, a speech service, an asynchronous 3.1 kHz bearer service (modem), an asynchronous UDI bearer service and a facsimile Group 3 teleservice, which means that the subscriber needs four MSISDN numbers. The plurality of MSISDN numbers is problematic both for the user and the network operator.
Networks where a terminal equipment of the fixed network is connected to the network via a radio connection instead of a subscriber cable are called wireless local loop (WLL) networks or radio local loop (RLL) networks. A WLL may be based on a mobile network, such as the GSM. There are several configurations by means of which a GSM-based WLL system can be implemented. FIG. 2 shows a configuration where the GSM network is used as such. Instead of a normal mobile station (MS), the terminal equipment comprises a fixed subscriber base station 22 at the subscriber's premises and a PSTN telephone 21 connected to the subscriber base station 22. FIG. 3 in turn shows a configuration where a base station controller (BSC), an MSC, an HLR and a visitor location register VLR in the GSM network are replaced with a WLL-specific network element, i.e. a WLL access node. The WLL access node may contain for example the following functions: transcoding, echo cancellation, basic functions of the location registers (VLR, HLR) and adaptation functions (IWF) for data services. In each case, an IWF is required at the network side (in the MSC or the WLL access node) if data services are supported.
Such a large number of services and protocols creates difficulties for network operators and users. In order for a mobile subscriber to be able to make and receive calls requiring different protocols, he must order several network services from the network operator. For the operator it is problematic that each subscriber needs a plurality of MSISDN numbers, which uses up the numbering space of the network. Also, definition of the services in the network databases consumes the capacity of the databases.